1. Field of the Invention
The present invention relates to a self-propelled working vehicle. Particularly, it relates to a self-propelled working vehicle of the type which includes an engine, a working implement driven by the engine, and a road wheel or catapillar driven by the engine.
2. Description of Relevant Art
There are known self-propelled working vehicles of the type which includes an engine, a working implement driven by the output of the engine, and a road wheel driven by the same, such as proposed in the U.S. Pat. No. 3,580,351 by I. J. Mollen.
In the U.S. Patent by Mollen, the working implement is given in the form of the combination of a snow-gathering device and a snow-blowing device.
In other words, the U.S. Patent by Mollen has disclosed a self-propelled working vehicle in the form of a snow-removing tractor including a power transmitting system diagrammatically shown in the attached "prior art" drawing FIG. 5.
In FIG. 5, designated at reference numeral 200 is the power transmitting system. The power transmitting system 200 is provided with an engine 201 having a crankshaft 202 arranged in the longitudinal or fore to aft direction of the vehicle. The engine power as output from the crankshaft 202 is transmitted by means of a drive pulley 203 mounted on one end of the crankshaft 202, through a drive belt 204 trained by the drive pulley 203, to a driven pully 205 mounted on the rear end of a shaft 208 as a drive shaft of a working implement having a snow-gathering auger 206 and a snow blower 207, thereby driving the combination of the auger 206 and the blower 207 to work as an implement for snow removal.
Moreover, the crankshaft 202 is adapted to drive, through a gear train 209, a cam shaft 210 having mounted on one end thereof another drive pulley 211 for training another drive belt 212. The engine power as output via the drive belt 212 is transmitted by means of a main transmission 213 to an axle 221 of a driving road wheel 222. The main transmission 213, which is arranged longitudinally of the vehicle, includes a drive shaft 214 having mounted on the front end thereof a driven pulley 215 driven by the drive belt 212 and on the rear end thereof a drive disc 216 extending transversely of the vehicle and a driven shaft 217 arranged perpendicularly to the drive shaft 214, i.e. in the transverse direction of the vehicle, the driven shaft 217 having at either end thereof a friction disc 218 axially slidably splined thereon and brought into frictional engagement with the drive disc 216 and at the other end thereof an output gear 219 mounted thereon.
The friction disc 218 has on the circumference thereof an elastic ring 223 fixed thereto and adapted to effect the frictional engagement with the drive disc 216, thereby to transmit the necessary driving power from the disc 216 to the disc 218. The speed shifting of the driving wheel 222 is effectable in a well-known manner, i.e., by first retreating the drive disc 216 to thereby release the friction disc 218 from the frictional engagement therewith and, then, properly shifting the friction disc 218 along the driven shaft 217, before advancing the drive disc 216 to thereby bring the friction disc 218 again into the frictional engagement therewith.
Although, when such snow-removing tractor is moving on the snow of which accumulation may be uneven depending such as on the ground surface and snow-fall condition, the load in the form of a torque its main transmission is subjected to varies according to the unevenness of snow accumulation, such variation can be effectively absorbed by the main transmission which is of a friction disc type as described above.
However, such snow-removing tractor is adapted to proceed performing a snow-removal work, thus having its running speed preset to be remarkably low as of a vehicle, i.e. as low as a walking speed of man, so that the movment to and from the working place must be very slow.
To overcome such shortcoming, the main transmission 213 may be first modified by enlarging the diameter of the drive disc 216 as well as the travel range of the friction disc 218. Such modification, however, is to unavoidably extend the dimensions of the transmission itself, thus scaling up the snow-removing tractor. In this respect, when taking into consideration the load variation attendant the running on the snow, it may be most favorable to employ the friction disc type transmission which is able to be adapted with a relatively simple construction to cope with the load variation. However, for the dimensional parameters of such conventional transmission are determined to be best effective at a very low moving speed, which implies that any modification such as by the enlargement of drive disc diameter may not bring into existence more than the lowerment in the durability of such transmission. This is because expanding the running speed range of snow-removing tractor in such a manner as described above is to expand the reduction gear ratio of transmission, which means subjecting a friction disc thereof to larger torques.
In other words, it may be considerably difficult to expand the running speed range of such snow-removing tractor without marring the inherent function of its friction disc type transmission and without enlarging the size thereof.
On the other hand, as a second possible modification, also the interposition of a sub-transmission between the main transmission 213 and the driving road wheel 222 may serve to expand the running speed range of the snow-removing tractor. Such interposition, however, is to again give rise to an expansion of the reducing gear ratio of power transmission system similarly to the case of the foregoing modification, thus causing the main transmission to be directly subjected to an increasing torque in reverse proportion to the gear ratio expansion, which is unfavorable to the durability of the main transmission.
In this respect also, it may be considerably difficult to expand the running speed range of a conventional snow-removing tractor having a friction disc type transmission, without giving such unfavorable effect on the durability of the transmission.
The present invention has been achieved to effectively overcome such conventional problems of a self-propelled working vehicle, particularly of a snow-removing tractor vehicle.